Abstract:

The advent of a soil health as a framework for management of row crops in the U.S. Midwest has major implications for agronomic practices. A soil health approach posits a new set of priorities for assessing soil compared to traditional forms of soil testing and resultant management recommendations. Our work examined soil health testing as a means to soil management using three distinct approaches. First, we worked with farmers across the state of Michigan to compare traditional field crop tests with results from soil health tests across a range of farmer fields, to compare how each test captured information related to soil management. Second, we evaluated an additional soil health assay for soil nitrification potential, to compare how this important biological process varied both along an experimental gradient of nitrogen application rates and across farmer fields. Finally, we held interviews with all growers to discuss how they understood the soil test results, and how this information fit with their own experience of managing individual fields. We found that soil health test results described a broad range of soil parameters that characterized differences in physical and biological properties on farmer fields. Compared to traditional soil tests, soil health tests were superior in revealing both positive parameters on good fields and constraints on poor fields, but also showed important limitations for some parameters such as soil compaction. A soil health assay for soil nitrification potential revealed clear increases in the magnitude of this process with increasing N fertilization, and concomitant increases in the microbial populations responsible for nitrification. Measuring nitrification potential on farmer fields suggested a possible new tool for assessing nitrogen management for improved agronomic and environmental outcomes. Finally, soil health test results elicited distinctly broader discussions with growers regarding soil management, compared to traditional soil test results. Growers compared and contrasted soil health results with their own management experience of individual fields and found them more informative to their understanding of specific fields than traditional soils tests. However, growers were less sure how to act on soil health test results. Nearly all growers appreciated the new information and wanted to continue monitoring soil health to help inform management decisions.

Introduction:

Row crop growers in Michigan and throughout the U.S. Midwest manage their fields for multiple outcomes from yield to profitability to environmental quality. To do this, they rely on many kinds of knowledge, including their own experience and information from outside sources such as crop advisers and soil testing agencies. Currently, soil testing is undergoing a major shift in emphasis, from managing for individual inputs/deficits of key nutrients, to overall soil management, a holistic approach often termed soil health. Soil health test parameters continue to evolve, but they differ from traditional soil tests in methodology and in the recommended management guidelines which follow from test results compared to traditional soil tests. Farmer decisions based on soil health test output may fit into a broader management framework, including tillage practices, residue management, or crop rotation. Thus, it is critical that soil health tests provide accurate, field-specific data which farmers can rely for these decisions. In contrast, traditional soil test have generated decades of fine scale data (i.e. recommendations for specific crops in specific counties). Soil health tests are still in the early stages of implementation and need to be vigorously tested. While soil health parameters have proven to be management-sensitive through research, this may not ensure that soil tests capture important differences on farmer fields, or in distinct regions such as those in Michigan. Finally, even if soil health tests accurately capture variability in soil physical, biological and chemical parameters on farmer fields, ultimately the manner in which farmers interpret and implement agronomic decisions based on these results is key to a soil health management framework, and whether it leads to positive agronomic performance for farmers.

Our work assesses multiple components of adapting soil health testing to Michigan. We worked with row crop farmers in three distinct regions of Michigan and asked them to identify four fields to sample for soil health testing, based on their judgment of ‘Best’ and “Worst” fields, a non-row crop (NRC) field, such as a woodlot or hay field, and an additional ‘Choice’ field which they wished to test. In so doing we wished to capture a range of field variability as identified by growers through their own management experience. We ran soil health tests alongside traditional field crop tests for each field. In addition we assessed nitrification potential as a possible additional soil health assay by measuring this process on these fields and on controlled experimental plots. Finally, we discussed test results with each grower to understand how well soil health results reflected their own management practices for each field type.

Project objectives:

This work addressed three targets assessing soil health management on Michigan farms. First we analyzed the efficacy of soil health tests parameters across a range of Michigan farms. We also evaluated a test for nitrification potential as a new assay aimed at nitrogen management, on a controlled experimental gradient and on four farm fields. Finally we discussed soil test results with growers to assess how they understood test results and interpreted management options for their own fields. Specifically we sought to:

Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture or SARE.

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